26 March] 1872 – 4 August 1940) was a Russian author, essayist, literary critic, religious thinker, newspaper editor and political activist, best known for his role in the influential early 1900s Mir Iskusstva circle and part of quasi-religious Troyebratstvo (The Brotherhood of Three), along with two of his closest friends and spiritual allies, Dmitry Merezhkovsky and Zinaida Gippius.

It was at this time that his close friendship with Dmitry Merezhkovsky and Zinaida Gippius began; soon he joined them to form "Troyebratstvo", a quasi-religious group which some saw as a domestic sect, claiming to aim at renovating the Christian values along the new, modernist lines.

Instead, along with Boris Savinkov, the notorious terrorist-turned-novelist he struck up a friendship with, Filosofov chose to stay in Warsaw to begin working on the reformation of the White Army on the territory of Poland.

He was a coordinator of Russian Political Committee, one of the leaders of the People's Union for the Defence of Motherland and Freedom, and Józef Piłsudski's counsellor.

Choosing to stay in Poland, but visiting Paris occasionally, Filosofov edited numerous Russian immigrant newspapers, including Svoboda (Freedom, 1920–1921), Za Svobodu (1921–1932), Molva (People's Talk, 1932–1934), co-edited Paris-Warsaw magazine Myech (Sword, 1934–1939).